This invention relates to an improved control system for rotary gas and oil burners of the type described, for example, in U.S. Pat. Nos. 2,177,225; 2,351,421 and the like. In this respect, such burners produce rotary motion by discharge of gaseous or atomized liquid fuel under pressure; and, the rotary or "fan" motion serves not only for propulsion of combustion-supporting air, but also for effecting an intimate and homogeneous admisture of fuel and air.
FIG. 1 illustrates a typical rotary burner of the type with which the invention finds particular utility. Therein, a main shaft 10 is mounted for rotary motion within suitable bearings, not shown; and, steam and gas or a liquid fuel such as oil are directed through passageways 12, 14, 16, and 17 located within the shaft 10. Typical structures also include suitable controls so that the burner can be selectively fueled by either liquid or gaseous fluids. For purposes of simplicity, however, such details are not shown in the FIG. 1 schematic illustration.
In the typical rotary burner the steam lines include one or more venturi sections 18 having a throat portion 20 and a diffuser portion 22 which is connected through channels such as 24 to outlet ports 26 in arms 28 connected to a fan, not shown. In this manner, the fuel, steam and the fan's air are all directed into the flame zone 34 located to the left of the fan in the schematic illustration if FIG. 1. At the same time, steam is directed to a cavity 30 for cooling purposes.
In operation, as the steam passes through the throat 20 of the venturi 18 it is expected to pull oil through orifice 36 from passageway 16. The oil-steam mixture is then forced into the passageways 24 and out of ports 26, causing the fan to rotate and pull air into the flame zone 34.
Further details of suitable rotary burners can be found in publicly available trade publications such as Catalogue 500 A (March 1972) of the Coppus Engineering Corporation, 344 Park Avenue, Worcester, Mass. 01610; or Manual 230, published by the same corporation.
During operation of rotary burners, the flows of fuel, steam, and air are adjusted to provide stoichiometric mixtures or variations therefrom in order to provide the desired flame in the burn zone. These adjustments are conventionally initially performed manually in order to determine suitable "set points" for the burner controls with the expectation that, thereafter, the burner's various flow rates will be automatically adjusted as the burner's firing rate is changed. In this respect, particularly where the burner is fueled by oil, satisfactory operation requires that the steam pressure be higher than that of the fuel pressure as illustrated in FIG. 2; and, the required differential between the two pressures increases with the burner's firing rate (fuel flow). Hence, particularly with today's emphasis upon ecological considerations and the increased emphasis upon fuel economy, it is desired that the fuel-steam pressure differentials be accurately controlled during automatic operation so as to provide a low-smoke flame having high heat release.
One structure for controlling the steam-fuel pressure differential is illustrated in FIG. 3. Therein, a pressure differential sensor-transmittor 40 measures the pressure differential between fuel line 42 and steam line 44. Then, as the burner's firing rate is changed by means of a fuel pressure control valve 46, the steam pressure is adjusted by manual operation of a ratio controller 48 which operates through a pressure differential controller 50 to adjust a diaphragm-type steam-pressure control valve 52. In this respect, the ratio control 48 is initially manually adjusted by visual inspection of the burner flame over the full firing range of the burner. Thereafter, during desired automatic operation, as fuel pressure is changed to vary the burner's firing rate, the pressure differential controller 50 is expected to be operative in response to signals from the pressure differential sensor 40 and the ratio controller 48 to automatically adjust the steam pressure valve 52.
The FIG. 3 structure, however, is unstable so that efficient burner operation is sporadic. That is, fuel pressures tend to vary from those which are expected. Hence, a fuel pressure sensor and control mechanism 54 was inserted in the fuel control line 56 in an effort to adjust the setting of fuel pressure control valve 46 as the unstable fuel pressure changes from that which is desired.
Even the addition of a pressure controller such as 54, however, results in an unstable flame having less than the desired efficiency. A primary object of the instant invention, therefore, is to provide an improved method of automatically controlling a rotary burner wherein the instabilities of the above described systems are substantially eliminated; and, it is another object of the invention to provide an improved rotary burner control system wherein the costs thereof are not prohibitive. In this regard, one of the advantages of the structure about to be described is that it is not only price-competitive with prior devices, but provides more efficient control at less cost than the systems described above.